The present invention relates to the preservation of materials that are susceptible to degradation and methods for inhibiting the degradation of such materials.
Certain materials are sufficiently stable that they can be isolated, purified, and stored at room temperature. However, there are certain materials (e.g., chemically reactive and/or bioactive materials) that are not sufficiently stable to be stored long term without utilizing a more elaborate stabilization and/or storage procedure. For some materials, degradation can occur in terms of structural change and/or loss of activity or function as a result of isolation or upon storage. Such degradation often occurs in two settings: under the stresses of processing or isolating the material (e.g., mixing, heating, extracting, pumping, drying, freezing, distilling, extruding or the like), and under storage conditions (i.e., after isolation). For example, during drying or freezing processes, denaturation of proteins and destruction of liposome structure can occur. Upon storage (after drying or freezing), oxidation and free radical attack also can promote degradation of bioactive materials.
In some instances, it is desirable to stabilize and/or store certain materials in the presence of a preserving agent (i.e., a protective agent). It is advantageous to employ a preserving agent that has the ability to stabilize such materials under both isolation and storage conditions. In this respect, the preserving agent should have the ability to protect the material from degradation or loss of function under the stresses of isolation and also during storage.
Certain carbohydrates have been used as preserving agents for various bioactive materials (e.g., enzymes, tissues, organelles, and the like). The incorporation of certain bioactive materials in glassy or rubbery carbohydrate compositions is said to be an effective approach in stabilizing various chemically reactive materials, for example, as purportedly described in U.S. Pat. No. 5,098,893. The ability of carbohydrate compositions in the glassy state to stabilize bioactive materials also may be related to the glass transition temperature of the composition (see, e.g., Bell et al. Journal of Food Science, 61, 372-374 (1996)). Certain non-reducing sugars have been used as preserving agents in the stabilization of bioactive materials with varying degrees of success. For example, U.S. Pat. No. 5,290,765 purports to describe the use of sucrose in the protection of lysozyme enzyme from the stresses of air-drying, and also from the destructive reactions that can occur upon storage. Rossi et al., Biotechnol. Prog., 13, 609-618 (1997) purports to describe the use of trehalose and sucrose in the stabilization of enzyme EcoRI.
While certain sugars such as sucrose and trehalose are often deemed advantageous in connection with protection of certain materials, these sugars are deficient in certain respects. For example, sucrose is generally considered quite labile, and can convert to fructose and glucose. Trehalose has good preserving properties for certain bioactive materials, but the high cost of trehalose can limit its use as a preserving agent. Moreover, reduced (i.e. hydrogenated) sugars such as sorbitol or other low molecular weight hydrogenated starch hydrolysates, or other low molecular weight compounds lack certain functional properties relating, for example, to water binding, molecular weight, osmolality, viscosity, and the like and are thus unsuitable for use in connection with certain applications.
In view of the foregoing, there exists a need for a low-cost non-labile preserving agent, particularly a carbohydrate preserving agent, that is effective in the protection of materials that are susceptible to degradation and that is compatible with such materials. There also is a need for a method of protecting such materials against degradation during isolation and storage.
The present invention is predicated on the surprising discovery that reduced malto-oligosaccharides have preserving properties.
In accordance with the invention, a composition that includes a material that is susceptible to degradation and a preserving agent that comprises one or more reduced malto-oligosaccharide species in an amount effective to inhibit the degradation of the material is provided. By xe2x80x9cdegradationxe2x80x9d is contemplated a structural or chemical change in the material (such as chemical degradation or reaction with a carrier), and/or a loss of activity or function of the material (for instance, the loss of activity of an enzyme) or a change in conformation of a protein. The preserving agent of the present invention can include a single reduced malto-oligosaccharide species or plurality of such species. While the reduced malto-oligosaccharides used in conjunction with the present invention can be obtained by any suitable method, the malto-oligosaccharides are preferably prepared via reduction of readily available malto-oligosaccharide(s), e.g., as described in U.S. patent application Ser. No. 09/366,065 (corresponding to WO 99/36442).
A variety of materials can be preserved with reduced malto-oligosaccharides in accordance with the invention. Such materials include, for example, compounds that react with a carbohydrate carbonyl substituent such as an aldehyde substituent or ketone, photochemically reactive materials, materials that react upon exposure to atmospheric oxygen, oxidants, reducing agents, polymerizable materials, catalysts, coloring agents, flavoring agents, proteins, mixtures thereof, and the like, and precursors thereof, biological materials (e.g., tissues, cells (e.g., yeasts and organelles) and biologically active compounds (including mixtures thereof and precursors thereof). The reduced malto-oligosaccharides also may be used to preserve extracts (natural or synthetic) containing such materials as well as mixtures of such materials and precursors thereof. The composition of the present invention can be in any suitable form (e.g., granules, dry powder, solution, gel, glass, or the like).
The present invention further provides a method of preserving a material. In accordance with the invention, the method includes contacting the material with a preserving effective amount of preserving agent that comprises one or more reduced malto-oligosaccharide species, as well as a method of storing a material that comprises storing the composition formed upon contacting the material with the preserving agent. The composition can be stored in any suitable form, for example, as a solid composition, gel, glass, or rubbery substance.
These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.